octeontx2-af: Misc cleanups in cgx driver

* Do CGX init before NIX init
  This would add consistency in NIX code that depends on cgx ports

* Few other misc cleanups
  - rvu_cgx_probe renamed as rvu_cgx_init for consistency
  - rvu_cgx_exit wrapper added to take care of the exit path
  - Added error check on cgx_lmac_event_handler_init
  - Minor cleanups in cgx.h related to tab alignment
  - Removed redundant ids from enum cgx_cmd_id

Signed-off-by: Linu Cherian <lcherian@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>